1. Field of the Invention
The present invention relates to a cassette including a strip of medium with a mechanism for preventing loosening of the strip.
2. Background of the Related Art
A conventional cassette includes two reels rotatably mounted in parallel, and a strip of medium supplied from one of the two reels and taken up by the other reel. A mechanism is included to prevent the reel from rotating so that the strip may not be loosened when the cassette is not in use. In Japanese laid-open publication No. 60/23087, for example, a cassette case has an integral spring portion pressed against the side of a reel. The resulting friction prevents the strip from being loosened. Also, U.S. Pat. No. 4,687,358, and Japanese laid-open utility model publication No. 61/120552 disclose cassettes in which a flexible piece is pressed into the interior of a cassette case so as to make a reel free to rotate when in use. Japanese laid-open utility model publication No. 62/38163 discloses a cassette in which a reel includes a spring to make the reel free to rotate. In Japanese laid-open utility model publication No. 63/7558, a discrete stopper is inserted to prevent a strip of medium from being loosened. U.S. Pat. No. 4,883,234 discloses a cassette within which a rotation prevention piece extends between the front ends of lead springs.
However, in Japanese laid-open patent publication No. 60/23087, for example, a force is equally exerted when the cassette is in use and when the cassette is not in use. It is difficult to apply an appropriate amount of force in either case. The other prior art cassettes require a greater number of parts, are complicated in structure, and require more manufacturing processes. This makes it difficult to produce the cassettes and results in an increase in the production cost.